The 3rd Generation Partnership Project, 3GPP, is responsible for the standardization of the Universal Mobile Telecommunication System, UMTS, and Long Term Evolution, LTE. The 3GPP work on LTE is also referred to as Evolved Universal Terrestrial Access Network, E-UTRAN. LTE is a technology for realizing high-speed packet-based communication that can reach high data rates both in the downlink and in the uplink, and is thought of as a next generation mobile communication system relative to UMTS. LTE brings significant improvements in capacity and performance over previous radio access technologies and are being deployed extensively by operators to meet the increasing demand by consumers.
The modernization of antenna technologies in practice is moving forward in a high pace, which enables the use of more advance antenna setups and techniques in order to increase capacity and performance in a mobile radio network. With the development of modern Active Antenna Systems, AAS, several new capacity enhancing features are enabled. One of these features is the possibility to redefine cells. A cell in this context, hereinafter also referred to as a sector, is defined by a cell-specific reference signal, CRS, transmitted at a frequency carrier.
With the use of AASs, which are already available in practice, sectorization is made possible; splitting a single cell in the network into a plurality of cells or sectors. The use of sectorization is a well-established way to increase the capacity of a cellular network. By using directional radiation beam patterns, the coverage area is divided into several sectors. The different sectors are allowed to use the same time and frequency resources thereby increasing the capacity of the network. A standard deployment is to use three directional antennas per site, but other types of deployments are also foreseen.
With the introduction of adaptive antenna systems, AAS, wherein each antenna consists of a number of active elements, comes an ability to dynamically change sectorization so that each antenna can transmit several beams directed differently, and where each beam acts as a separate cell that can reuse the time and frequency resources. The sectorization is done in a horizontal and/or vertical plane, but a horizontal sectorization may of course also have an impact in a vertical plane and vice versa.
The gains that can be achieved with such sectorization are promising and seem to be of great importance to achieve the goals of future radio networks. The benefits from sectorization mainly come from the spatial reuse of resources and also from the interference reduction to the neighbours. However, there is also a cost of sectorization from inter-sector interference and reduction in transmission power per sector since the total amount of power available has to be shared between the sectors. Thus, sectorization is not always beneficial.
The leveraging of the benefit and cost is an important aspect for successful sectorization. It is known that the user distribution can help in taking a sectorization or antenna reconfiguration decision; see e.g. 3GPP TSG-RAN WG3 Meeting #86, San Francisco, USA, Nov. 17-21, 2014, R3-142715—Load information enhancements for AAS reconfiguration decisions, disclosing how a decision to sectorize or not to sectorize is based on fixed thresholds.
Existing methods also include acquiring information about the load of different sectors by sending out beam-formed reference signals, such as DRS or CSI-RS, and decide cell association of UEs based on measurement reports obtained from those reference signals. Using DRS/CSI-RS for acquiring estimates about UE serving sectors will create some overhead. Further, in case of a high number of possible sector configurations, many configurations need be tried. Further, it is not supported by legacy UEs.
There is a need for improved adherence between sector set up and traffic situation in a wireless network; an improved ability to adapt sectorization decisions to user distribution.